Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Computing devices such as personal computers, laptop computers, tablet computers, cellular phones, and countless types of Internet-capable devices are increasingly prevalent in numerous aspects of modern life. As such, the demand for data connectivity via the Internet, cellular data networks, and other such networks, is growing. However, there are many areas of the world where data connectivity is still unavailable, or if available, is unreliable and/or costly.
Free space optical communication links can be formed between respective communication terminals that send and receive modulated laser light. For example, a first terminal may generate laser light modulated according to output data and transmit the laser light to a second terminal where the laser light is detected and demodulated to recover the data. Similarly, the second terminal may generate laser light modulated according to data and transmit laser light to the first terminal where the laser light is detected and demodulated.
To support full duplex communication in which data can be sent and received simultaneously using a single terminal, configurations may transmit data using a first wavelength and receive data using a second wavelength. The communication terminal can then include a dichroic beam splitter in the optical path from the primary aperture of the terminal. The dichroic beam splitter can allow one of the wavelengths to pass through and reflect the other to thereby separate the light sent/received at the two different wavelengths while sharing a single primary aperture. For instance, a first terminal can be configured to transmit at wavelength 1 and receive at wavelength 2. A dichroic beam splitter may pass wavelength 1 and reflect wavelength 2. A laser light source configured to emit at wavelength 1 can be situated to emit light that passes through the dichroic beam splitter, toward the primary aperture. A photo detector configured to detect at wavelength 2 can be situated to receive light that is reflected by the dichroic beam splitter after being received via the primary aperture. Similarly, a second communication terminal can be configured to transmit at wavelength 2 and receive at wavelength 1. A suitable laser light source and photo detector can be arranged with respect to a dichroic beam splitter to direct light to/from a single primary aperture of the second terminal. As such, the first and second communication terminals can communicate data in either direction simultaneously by sending and receiving modulated laser beams at the two different wavelengths.
To ensure alignment between spatially separated terminals, each terminal generally incorporates one or more adjustable beam steering mirrors that direct laser light to and from the respective transmit/receive apertures to the various laser light sources and photo detectors in each terminal. Adjusting orientations of the beam steering mirror(s) may then adjust the positions of various focal points in the optical path(s) coupling various laser light source(s) and photo detector(s) to the primary aperture. A feedback system may also be used to detect an angle of arrival of incoming laser light (e.g., from another terminal), and use the determined angle as feedback to direct transmitted laser light (e.g., to the other terminal). The optical path between the primary aperture and the various laser light source(s) and/or photo detector(s) may additionally include a variety of filters, mirrors, lenses, apertures, and other optical transmission components as necessary.